Immobilization of bacteriophage in wound-dressing nanostructure

Chitosan-based matrix as a carrier for bacteriophages

Wound healing is a dynamic and complex process where infection prevention is essential. Chitosan, thanks to its bactericidal activity against gram-positive and gram-negative bacteria, as well as anti-inflammatory and hemostatic properties, is an excellent candidate to design dressings for difficult-to-heal wound treatment. The great advantage of this biopolymer is its capacity to be chemically modified, which allows for the production of various functional forms, depending on the needs and subsequent use. Moreover, chitosan can be an excellent polymer matrix for bacteriophage (phage) packing as a novel alternative/supportive antibacterial therapy approach. This study is focused on the preparation and characteristics of chitosan-based material in the form of a film with the addition of Pseudomonas lytic phages (KTN4, KT28, and LUZ19), which would exhibit antibacterial activity as a potential dressing that accelerates the wound healing. We investigated the method of producing a polymer based on microcrystalline chitosan (MKCh) to serve as the matrix for phage deposition. We described some important parameters such as average molar mass, swelling capacity, surface morphology, phage release profile, and antibacterial activity tested in the Pseudomonas aeruginosa bacterial model. The chitosan polysaccharide turned out to interact with phage particles immobilizing them within a material matrix. Nevertheless, with the high hydrophilicity and swelling features of the prepared material, the external solution of bacterial culture was absorbed and phages went in direct contact with bacteria causing their lysis in the polymer matrix. KEY POINTS: • A novel chitosan-based matrix with the addition of active phages was prepared • Phage interactions with the chitosan matrix were determined as electrostatic • Phages in the matrix work through direct contact with the bacterial cells.

Comparing Methods to Genetically Engineer Bacteriophage and Increase Host Range

INTRODUCTION

Antibacterial resistance is an emerging problem in military medicine. Disruptions to the health care systems in war-torn countries that result from ongoing conflict can potentially exacerbate this problem and increase the risk to U.S. forces in the deployed environment. Therefore, novel therapies are needed to mitigate the impact of these potentially devastating infections on military operations. Bacteriophages are viruses that infect and kill bacteria. They can be delivered as therapeutic agents and offer a promising alternative to traditional antibiotic chemotherapy. There are several potential benefits to their use, including high specificity and comparative ease of use in the field setting. However, the process of engineering phages for military medical applications can be a laborious and time-consuming endeavor. This review examines available techniques and compares their efficacy.

MATERIALS AND METHODS

This review evaluates the scientific literature on the development and application of four methods of bacteriophage genome engineering and their consideration in the context of military applications. Preffered Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed for a systematic review of available literature that met criteria for analysis and inclusion. The research completed for this review article originated from the United States Military Academy's library "Scout" search engine, which compiles results from 254 available databases (including PubMed, Google Scholar, and SciFinder). Particular attention was focused on identifying useful mechanistic insight into the nature of the engineering technique, the ease of use, and the applicability of the technique to countering the problem of antimicrobial resistance in the military setting.

RESULTS

A total of 52 studies were identified that met inclusion criteria following PRISMA guidelines. The bioengineering techniques analyzed included homologous recombination (12 articles), in vivo recombineering (9 articles), bacteriophage recombineering of electroporated DNA (7 articles), and the CRISPR-Cas system (10 articles). Rates of success and fidelity varied across each platform, and comparative benefits and drawbacks are considered.

CONCLUSIONS

Each of the phage engineering techniques addressed herein varies in amount of effort and overall success rate. CRISPR-Cas-facilitated modification of phage genomes presents a highly efficient method that does not require a lengthy purification and screening process. It therefore appears to be the method best suited for military medical applications.

Phage formulations and delivery strategies: Unleashing the potential against antibiotic-resistant bacteria

Bacterial control promoted by bacteriophages (phages) is an attractive tool in the face of the antibiotic crisis triggered by the exacerbated use of these drugs. Despite the growing interest in using these viruses, some gaps still need answers, such as the protection and delivery of phages. Some limitation points involve the degradation of phage proteins by enzymes or inactivation in low-pH environments. In this review, a literature search using keywords related to the field of virus delivery formulations was done to understand the current scenario of using delivery techniques and phage formulations. A total of 2096 raw results were obtained, which resulted in 140 publications after refinement. These studies were analyzed for main application techniques and areas, keywords, and countries. Of the total, 57% of the publications occurred in the last five years, and the encapsulation technique was the most used among the articles analyzed. As excipient agents, lactose, trehalose, mannitol, PEG, and Leucine stand out. The development of phage formulations, protection approaches, their delivery routes, and the knowledge about the best application strategy enables the use of these organisms in several sectors. It can act as a powerful tool against antibiotic-resistant bacteria.

Development of carrageenan-immobilized lytic coliphage vB_Eco2571-YU1 hydrogel for topical delivery of bacteriophages in wound dressing applications

Bacteriophages are employed as cost-effective and efficient antibacterial agents to counter the emergence of antibiotic-resistant bacteria and other host bacteria in phage therapy. The increasing incidence of skin wounds is a significant concern in clinical practice, especially considering the limitations of antibiotic therapy. Furthermore, the lack of an effective delivery system that preserves the stability of bacteriophages hampers their clinical implementation. In recent years, there has been a growing amount of research on bacteriophage applications in veterinary and biomedical sciences. In our study, lytic coliphage vB_Eco2571-YU1 was isolated against pathogenic Escherichia coli host bacteria, and hydrogel wound dressing materials were fabricated with marine polysaccharide carrageenan (carr-vB_Eco2571-YU1) for their antibacterial activity. Transmission electron microscopy (TEM) morphology identified it as a Myoviridae coliphage with an icosahedral head length and width of approximately 60 and 56.8 nm, respectively, and a tail length of 119.7 nm. The one-step growth curve of coliphage revealed a latent period of 10 min, a rise period of 15 min, and a burst size of 120 virions per cell. The bacteriolytic activity of unimmobilized coliphages was observed within 2 h; however, strain-specific phage resistance was acquired after 9 h. In contrast, carr-vB_Eco2571-YU1 showed a sharp decline in the growth of bacteria in the log phase after 2 h and did not allow for the acquisition of phage resistance by the E. coli strain. The stability of coliphage under different pH, temperature, osmolarity, detergents, and organic solvents was evaluated. We also studied the long-term storage of carr-vB_Eco2571-YU1 hydrogels at 4 °C and found that the titer value decreased during a time-dependent period of 28 days. These hydrogels were also found to be hemocompatible using a hemolysis assay. The addition of plasticizer (0.6 % (w/v)) to the carrageenan (2 % (w/v)) to prepare carr-vB_Eco2571-YU1 hydrogels showed a decrease in compressive strength with enhanced elasticity. This phage therapy using polymeric immobilization of bacteriophages is a promising next-generation wound dressing biomaterial alternative to conventional wound and skin care management.

Monomeric streptavidin phage display allows efficient immobilization of bacteriophages on magnetic particles for the capture, separation, and detection of bacteria

Immobilization of bacteriophages onto solid supports such as magnetic particles has demonstrated ultralow detection limits as biosensors for the separation and detection of their host bacteria. While the potential impact of magnetized phages is high, the current methods of immobilization are either weak, costly, inefficient, or laborious making them less viable for commercialization. In order to bridge this gap, we have developed a highly efficient, site-specific, and low-cost method to immobilize bacteriophages onto solid supports. While streptavidin-biotin represents an ideal conjugation method, the functionalization of magnetic particles with streptavidin requires square meters of coverage and therefore is not amenable to a low-cost assay. Here, we genetically engineered bacteriophages to allow synthesis of a monomeric streptavidin during infection of the bacterial host. The monomeric streptavidin was fused to a capsid protein (Hoc) to allow site-specific self-assembly of up to 155 fusion proteins per capsid. Biotin coated magnetic nanoparticles were functionalized with mSA-Hoc T4 phage demonstrated in an E. coli detection assay with a limit of detection of < 10 CFU in 100 mLs of water. This work highlights the creation of genetically modified bacteriophages with a novel capsid modification, expanding the potential for bacteriophage functionalized biotechnologies.

Recent advances in bacteriophage-based therapeutics: Insight into the post-antibiotic era

Antibiotic resistance is one of the biggest threats to global health, as it can make the treatment of bacterial infections in humans difficult owing to their high incidence rate, mortality, and treatment costs. Bacteriophage, which constitutes a type of virus that can kill bacteria, is a promising alternative strategy against antibiotic-resistant bacterial infections. Although bacteriophage therapy was first used nearly a century ago, its development came to a standstill after introducing the antibiotics. Nowadays, with the rise in antibiotic resistance, bacteriophage therapy is in the spotlight again. As bacteriophage therapy is safe and has significant anti-bacterial activity, some specific types of bacteriophages (such as bacteriophage phiX174 and Pyo bacteriophage complex liquid) entered into phase III clinical trials. Herein, we review the key points of the antibiotic resistance crisis and illustrate the factors that support the renewal of bacteriophage applications. By summarizing recent state-of-the-art studies and clinical data on bacteriophage treatment, we introduced (i) the pharmacological mechanisms and advantages of antibacterial bacteriophages, (ii) bacteriophage preparations with clinical potential and bacteriophage-derived anti-bacterial treatment strategies, and (iii) bacteriophage therapeutics aimed at multiple infection types and infection-induced cancer treatments. Finally, we highlighted the challenges and critical perspectives of bacteriophage therapy for future clinical development.

Nanofiber Carriers of Therapeutic Load: Current Trends

The fast advancement in nanotechnology has prompted the improvement of numerous methods for the creation of various nanoscale composites of which nanofibers have gotten extensive consideration. Nanofibers are polymeric/composite fibers which have a nanoscale diameter. They vary in porous structure and have an extensive area. Material choice is of crucial importance for the assembly of nanofibers and their function as efficient drug and biomedicine carriers. A broad scope of active pharmaceutical ingredients can be incorporated within the nanofibers or bound to their surface. The ability to deliver small molecular drugs such as antibiotics or anticancer medications, proteins, peptides, cells, DNA and RNAs has led to the biomedical application in disease therapy and tissue engineering. Although nanofibers have shown incredible potential for drug and biomedicine applications, there are still difficulties which should be resolved before they can be utilized in clinical practice. This review intends to give an outline of the recent advances in nanofibers, contemplating the preparation methods, the therapeutic loading and release and the various therapeutic applications.

Incorporation of Mycobacteriophage Fulbright into Polycaprolactone Electrospun Nanofiber Wound Dressing

The Genus Mycobacterium includes pathogens known to cause disease in mammals such as tuberculosis (Mycobacterium tuberculosis) and skin infections (M. abscessus). M. smegmatis is a model bacterium that can cause opportunistic infections in human tissues and, rarely, a respiratory disease. Due to the emergence of multidrug-resistant bacteria, phage therapy is potentially an alternative way of treating these bacterial infections. As bacteriophages are specific to their bacterial host, it ensures that the normal flora is unharmed. Fulbright is a mycobacteriophage that infects the host bacteria M. smegmatis. The main goal of this study is to incorporate Mycobacteriophage Fulbright into a polycaprolactone (PCL) nanofiber and test its antimicrobial effect against the host bacteria, M. smegmatis. Stability tests conducted over 7 days showed that the phage titer does not decrease when in contact with PCL, making it a promising vehicle for phage delivery. Antimicrobial assays showed that PCL_Fulbright effectively reduces bacterial concentration after 24 h of contact. In addition, when stored at -20 °C, the phage remains viable for up to eleven months in the fiber. Fulbright addition on the nanofibrous mats resulted in an increase in water uptake and decrease in the mechanical properties (strength and Young's modulus) of the membranes, indicating that the presence of phage Fulbright can greatly enhance the physical and mechanical properties of the PCL. Cytotoxicity assays showed that PCL_Fulbright is not cytotoxic to Balbc/3T3 mouse embryo fibroblast cell lines; thus, phage-incorporated PCL is a promising alternative to antibiotics in treating skin infections.

Antibiofilm Efficacy of the Pseudomonas aeruginosa Pbunavirus vB_PaeM-SMS29 Loaded onto Dissolving Polyvinyl Alcohol Microneedles

Resistant bacteria prevail in most chronic skin wounds and other biofilm-related topical skin infections. Bacteriophages (phages) have proven their antimicrobial effectiveness for treating different antibiotic-resistant and multidrug-resistant bacterial infections, but not all phages are effective against biofilms. Phages possessing depolymerases can reach different biofilm layers; however, those that do not have depolymerase activity struggle to penetrate and navigate in the intricate 3D biofilm structure and mainly infect bacteria lodged in the outer biofilm layers. To address this, Pseudomonas aeruginosa phage vB_PaeM-SMS29, a phage with poor antibiofilm properties, was incorporated into polyvinyl alcohol (PVA, Mowiol 4:88) supplemented with 0.1% (v/v) of glycerol, and cast onto two different microneedle arrays varying in geometry. The dissolving microneedles were thoroughly characterized by microscopy, force-displacement, swelling, phage release and stability. Furthermore, 48 h-old biofilms were formed using the colony biofilm procedure (absence of broth), and the antibiofilm efficacy of the phage-loaded microneedles was evaluated by viable cell counts and microscopy and compared to free phages. The phages in microneedles were fairly stable for six months when stored at 4 °C, with minor decreases in phage titers observed. The geometry of the microneedles influenced the penetration and force-displacement characteristics but not the antimicrobial efficacy against biofilms. The two PVA microneedles loaded with phages reduced P. aeruginosa PAO1 biofilms by 2.44 to 2.76 log₁₀ CFU·cm^-2 at 24 h. These values are significantly higher than the result obtained after the treatment with the free phage (1.09 log₁₀ CFU·cm^-2). Overall, this study shows that the distribution of phages caused by the mechanical disruption of biofilms using dissolving microneedles can be an effective delivery method against topical biofilm-related skin infections.

[Local management of purulent wounds with wound dressings]

Purulent-inflammatory lesions of skin and soft tissues account for 30-35% of causes of admission to surgical hospitals. In outpatient system, this value reaches 35-60%. Moreover, suppuration of wounds after elective surgery occurs in 2-5% of cases. Adequately selected drugs for local wound therapy can achieve localization of purulent process and avoid spread of infection. This review summarizes data on development, experimental and clinical testing of wound dressings over the past 10 years, presents classification options and analyzes their advantages and disadvantages. The authors emphasize higher efficacy of hydrophilic coatings, and coatings based on chitosan, collagen, methylcellulose and its derivatives are preferred. It is advisable to introduce a component with antimicrobial, anesthetic and hemostatic activity stimulating tissue regeneration into the matrix of wound dressing. The priority is introduction of antiseptic substances causing fewer side effects compared to antibiotics. Further research and development of new wound dressings is a priority in surgery considering changing landscape and development of resistance of microorganisms.

Nanotechnology Based Approaches in Phage Therapy: Overcoming the Pharmacological Barriers

With the emergence and spread of global antibiotic resistance and the need for searching safer alternatives, there has been resurgence in exploring the use of bacteriophages in the treatment of bacterial infections referred as phage therapy. Although modern phage therapy has come a long way as demonstrated by numerous efficacy studies but the fact remains that till date, phage therapy has not received regulatory approval for human use (except for compassionate use).Thus, to hit the clinical market, the roadblocks need to be seriously addressed and gaps mended with modern solution based technologies. Nanotechnology represents one such ideal and powerful tool for overcoming the pharmacological barriers (low stability, poor in-vivo retention, targeted delivery, neutralisation by immune system etc.) of administered phage preparations.In literature, there are many review articles on nanotechnology and bacteriophages but these are primarily focussed on highlighting the use of lytic and temperate phages in different fields of nano-medicine such as nanoprobes, nanosensors, cancer diagnostics, cancer cell targeting, drug delivery through phage receptors, phage display etc. Reviews specifically focused on the use of nanotechnology driven techniques strictly to improve phage therapy are however limited. Moreover, these review if present have primarily focussed on discussing encapsulation as a primary method for improving the stability and retention of phage(s) in the body.With new advances made in the field of nanotechnology, approaches extend from mere encapsulation to recently adopted newer strategies. The present review gives a detailed insight into the more recent strategies which include 1) use of lipid based nano-carriers (liposomes, transfersomes etc.) 2) adopting microfluidic based approach, surface modification methods to further enhance the efficiency and stability of phage loaded liposomes 3) Nano- emulsification approach with integration of microfluidics for producing multiple emulsions (suitable for phage cocktails) with unique control over size, shape and drop morphology 4) Phage loaded nanofibers produced by electro-spinning and advanced core shell nanofibers for immediate, biphasic and delayed release systems and 5) Smart release drug delivery platforms that allow superior control over dosing and phage release as and when required. All these new advances are aimed at creating a suitable housing system for therapeutic bacteriophage preparations while targeting the multiple issues of phage therapy i.e., improving phage stability and titers, improving in-vivo retention times, acting as suitable delivery systems for sustained release at target site of infection, improved penetration into biofilms and protection from immune cell attack. The present review thus aims at giving a complete insight into the recent advances (2010 onwards) related to various nanotechnology based approaches to address the issues pertaining to phage therapy. This is essential for improving the overall therapeutic index and success of phage therapy for future clinical approval.

Viability of Bacteriophages in the Complex Hydrogel Wound Dressings in vitro

Using bacteriophages to overcome the increasing resistance of microorganisms to antibiotics is a novel research venue of clinical importance. Among other challenges, this technique is expected to create and maintain an adequate local concentration of bacteriophages at the site of application. In addition, the possibility of combining the phage preparation with antioxidants and anesthetics may provide new options for stimulating the reparative process. The aim of the study was to assess the viability and lytic activity of bacteriophages incorporated into a hydrogel-based wound dressing that contains polyvinyl alcohol, phosphate buffer, with optional additions of succinic acid and lidocaine.

Materials and Methods

A technique for incorporating bacteriophages into the complex hydrogel wound dressing ex tempore has been proposed. The bacteriolytic activity of phages inside the hydrogel was determined using standard microbiological techniques. Specifically, we used nutrient media with lawn cultures of Staphylococcus aureus added with the following antibacterial combinations: bacteriophages + succinic acid, bacteriophages + lidocaine, and bacteriophages + succinic acid + lidocaine. The lytic activity of bacteriophages was assessed within 1 to 7 days after the formation of the hydrogel.

Results

In all samples containing bacteriophages, the presence of viable and lytically active phages was noted within 1 to 7 days, as evidenced by the "negative colonies" on the culture lawns. On days 1 to 3, no secondary growth was recorded in the phage-containing samples. In hydrogel samples containing phages, succinic acid, and lidocaine, secondary bacterial colonies were detected starting from day 4 indicating some reduction in the lytic activity.

Conclusion

The results suggest that bacteriophages immobilized in the hydrogel maintain their viability and lytic activity, and this activity persists when the phages are combined with succinic acid and lidocaine.

Nano Iron Oxide-PCL Composite as an Improved Soft Tissue Scaffold

Iron oxide nanoparticles were employed to fabricate a soft tissue scaffold with enhanced physicochemical and biological characteristics. Growth promotion effect of L-lysine coated magnetite (Lys@Fe3O4) nanoparticles on the liver cell lines was proved previously. So, in the current experiment these nanoparticles were employed to fabricate a soft tissue scaffold with growth promoting effect on the liver cells. Lys@Fe3O4 nanoparticles were synthesized via co-precipitation reaction. Resulted particles were ~7 nm in diameter and various concentrations (3, 5, and 10 wt%) of these nanoparticles were used to fabricate nanocomposite PCL fibers. Electrospinning technique was employed and physicochemical characteristics of the resulted nanofibers were evaluated. Electron micrographs and EDX-mapping analysis showed that nanoparticles were well dispersed in the PCL fibers and no bead structure were formed. As expected, incorporation of Lys@Fe3O4 to the PCL nanofibers resulted in a reduction in hydrophobicity of the scaffold. Nanocomposite scaffolds were shown increased tensile strength with increasing concentration of employed nanoparticles. In contrast to PCL scaffold, nearly 150% increase in the cell viability was observed after 3-days exposure to the nanocomposite scaffolds. This study indicates that incorporation of magnetite nanoparticles in the PCL fibers make them more prone to cell attachment. However, incorporated nanoparticles can provide the attached cells with valuable iron element and consequently promote the cells growth rate. Based on the results, magnetite enriched PCL nanofibers could be introduced as a scaffold to enhance the biological performance for liver tissue engineering purposes.

Comparison of Delivery Methods in Phage Therapy against Flavobacterium columnare Infections in Rainbow Trout

Viruses of bacteria, bacteriophages, specifically infect their bacterial hosts with minimal effects on the surrounding microbiota. They have the potential to be used in the prevention and treatment of bacterial infections, including in the field of food production. In aquaculture settings, disease-causing bacteria are often transmitted through the water body, providing several applications for phage-based targeting of pathogens, in the rearing environment, and in the fish. We tested delivery of phages by different methods (via baths, in phage-coated material, and via oral delivery in feed) to prevent and treat Flavobacterium columnare infections in rainbow trout fry using three phages (FCOV-S1, FCOV-F2, and FCL-2) and their hosts (FCO-S1, FCO-F2, and B185, respectively). Bath treatments given before bacterial infection and at the onset of the disease symptoms were the most efficient way to prevent F. columnare infections in rainbow trout, possibly due to the external nature of the disease. In a flow-through system, the presence of phage-coated plastic sheets delayed the onset of the disease. The oral administration of phages first increased disease progression, although total mortality was lower at the end of the experiment. When analysed for shelf-life, phage titers remained highest when maintained in bacterial culture media and in sterile lake water. Our results show that successful phage therapy treatment in the aquaculture setting requires optimisation of phage delivery methods in vivo.

Strategies for Surface Immobilization of Whole Bacteriophages: A Review

Bacteriophage immobilization is a key unit operation in emerging biotechnologies, enabling new possibilities for biodetection of pathogenic microbes at low concentration, production of materials with novel antimicrobial properties, and fundamental research on bacteriophages themselves. Wild type bacteriophages exhibit extreme binding specificity for a single species, and often for a particular subspecies, of bacteria. Since their specificity originates in epitope recognition by capsid proteins, which can be altered by chemical or genetic modification, their binding specificity may also be redirected toward arbitrary substrates and/or a variety of analytes in addition to bacteria. The immobilization of bacteriophages on planar and particulate substrates is thus an area of active and increasing scientific interest. This review assembles the knowledge gained so far in the immobilization of whole phage particles, summarizing the main chemistries, and presenting the current state-of-the-art both for an audience well-versed in bioconjugation methods as well as for those who are new to the field.

Evaluation of the Stability of Bacteriophages in Different Solutions Suitable for the Production of Magistral Preparations in Belgium

In Belgium, the incorporation of phages into magistral preparations for human application has been permitted since 2018. The stability of such preparations is of high importance to guarantee quality and efficacy throughout treatments. We evaluated the ability to preserve infectivity of four different phages active against three different bacterial species in five different buffer and infusion solutions commonly used in medicine and biotechnological manufacturing processes, at two different concentrations (9 and 7 log pfu/mL), stored at 4 °C. DPBS without Ca²⁺ and Mg²⁺ was found to be the best option, compared to the other solutions. Suspensions with phage concentrations of 7 log pfu/mL were unsuited as their activity dropped below the effective therapeutic dose (6–9 log pfu/mL), even after one week of storage at 4 °C. Strong variability between phages was observed, with Acinetobacter baumannii phage Acibel004 being stable in four out of five different solutions. We also studied the long term storage of lyophilized staphylococcal phage ISP, and found that the titer could be preserved during a period of almost 8 years when sucrose and trehalose were used as stabilizers. After rehydration of the lyophilized ISP phage in saline, the phage solutions remained stable at 4 °C during a period of 126 days.

Formulations for Bacteriophage Therapy and the Potential Uses of Immobilization

The emergence of antibiotic-resistant pathogens is becoming increasingly problematic in the treatment of bacterial diseases. This has led to bacteriophages receiving increased attention as an alternative form of treatment. Phages are effective at targeting and killing bacterial strains of interest and have yielded encouraging results when administered as part of a tailored treatment to severely ill patients as a last resort. Despite this, success in clinical trials has not always been as forthcoming, with several high-profile trials failing to demonstrate the efficacy of phage preparations in curing diseases of interest. Whilst this may be in part due to reasons surrounding poor phage selection and a lack of understanding of the underlying disease, there is growing consensus that future success in clinical trials will depend on effective delivery of phage therapeutics to the area of infection. This can be achieved using bacteriophage formulations instead of purely liquid preparations. Several encapsulation-based strategies can be applied to produce phage formulations and encouraging results have been observed with respect to efficacy as well as long term phage stability. Immobilization-based approaches have generally been neglected for the production of phage therapeutics but could also offer a viable alternative.

The clinical path to deliver encapsulated phages and lysins

The global emergence of multidrug-resistant pathogens is shaping the current dogma regarding the use of antibiotherapy. Many bacteria have evolved to become resistant to conventional antibiotherapy, representing a health and economic burden for those afflicted. The search for alternative and complementary therapeutic approaches has intensified and revived phage therapy. In recent decades, the exogenous use of lysins, encoded in phage genomes, has shown encouraging effectiveness. These two antimicrobial agents reduce bacterial populations; however, many barriers challenge their prompt delivery at the infection site. Encapsulation in delivery vehicles provides targeted therapy with a controlled compound delivery, surpassing chemical, physical and immunological barriers that can inactivate and eliminate them. This review explores phages and lysins' current use to resolve bacterial infections in the respiratory, digestive, and integumentary systems. We also highlight the different challenges they face in each of the three systems and discuss the advances towards a more expansive use of delivery vehicles.

Therapy of infected wounds: overcoming clinical challenges by advanced drug delivery systems

In recent years, the incidence of infected wounds is steadily increasing, and so is the clinical as well as economic interest in effective therapies. These combine reduction of pathogen load in the wound with general wound management to facilitate the healing process. The success of current therapies is challenged by harsh conditions in the wound microenvironment, chronicity, and biofilm formation, thus impeding adequate concentrations of active antimicrobials at the site of infection. Inadequate dosing accuracy of systemically and topically applied antibiotics is prone to promote development of antibiotic resistance, while in the case of antiseptics, cytotoxicity is a major problem. Advanced drug delivery systems have the potential to enable the tailor-made application of antimicrobials to the side of action, resulting in an effective treatment with negligible side effects. This review provides a comprehensive overview of the current state of treatment options for the therapy of infected wounds. In this context, a special focus is set on delivery systems for antimicrobials ranging from semi-solid and liquid formulations over wound dressings to more advanced carriers such as nano-sized particulate systems, vesicular systems, electrospun fibers, and microneedles, which are discussed regarding their potential for effective therapy of wound infections. Further, established and novel models and analytical techniques for preclinical testing are introduced and a future perspective is provided.

Encapsulation and Delivery of Therapeutic Phages

Delivery of therapeutic compounds to the site of action is crucial. While many chemical substances such as beta-lactam antibiotics can reach therapeutic levels in most parts throughout the human body after administration, substances of higher molecular weight such as therapeutic proteins may not be able to reach the site of action (e.g. an infection), and are therefore ineffective. In the case of therapeutic phages, i.e. viruses that infect microbes that can be used to treat bacterial infections, this problem is exacerbated; not only are phages unable to penetrate tissues, but phage particles can be cleared by the immune system and phage proteins are rapidly degraded by enzymes or inactivated by the low pH in the stomach. Yet, the use of therapeutic phages is a highly promising strategy, in particular for infections caused by bacteria that exhibit multi-drug resistance. Clinicians increasingly encounter situations where no treatment options remain available for such infections, where antibiotic compounds are ineffective. While the number of drug-resistant pathogens continues to rise due to the overuse and misuse of antibiotics, no new compounds are becoming available as many pharmaceutical companies discontinue their search for chemical antimicrobials. In recent years, phage therapy has undergone massive innovation for the treatment of infections caused by pathogens resistant to conventional antibiotics. While most therapeutic applications of phages are well described in the literature, other aspects of phage therapy are less well documented. In this review, we focus on the issues that are critical for phage therapy to become a reliable standard therapy and describe methods for efficient and targeted delivery of phages, including their encapsulation.

Kiwifruit bacterial canker: an integrative view focused on biocontrol strategies

Phage-based biocontrol strategies can be an effective alternative to control Psa-induced bacterial canker of kiwifruit. The global production of kiwifruit has been seriously affected by Pseudomonas syringae pv. actinidiae (Psa) over the last decade. Psa damages both Actinidia chinensis var. deliciosa (green kiwifruit) but specially the susceptible Actinidia chinensis var. chinensis (gold kiwifruit), resulting in severe economic losses. Treatments for Psa infections currently available are scarce, involving frequent spraying of the kiwifruit plant orchards with copper products. However, copper products should be avoided since they are highly toxic and lead to the development of bacterial resistance to this metal. Antibiotics are also used in some countries, but bacterial resistance to antibiotics is a serious worldwide problem. Therefore, it is essential to develop new approaches for sustainable agriculture production, avoiding the emergence of resistant Psa bacterial strains. Attempts to develop and establish highly accurate approaches to combat and prevent the occurrence of bacterial canker in kiwifruit plants are currently under study, using specific viruses of bacteria (bacteriophages, or phages) to eliminate the Psa. This review discusses the characteristics of Psa-induced kiwifruit canker, Psa transmission pathways, prevention and control, phage-based biocontrol strategies as a new approach to control Psa in kiwifruit orchards and its advantages over other therapies, together with potential ways to bypass phage inactivation by abiotic factors.

Phage therapy as a potential approach in the biocontrol of pathogenic bacteria associated with shellfish consumption

Infectious human diseases acquired from bivalve shellfish consumption constitute a public health threat. These health threats are largely related to the filter-feeding phenomenon, by which bivalve organisms retain and concentrate pathogenic bacteria from their surrounding waters. Even after depuration, bivalve shellfish are still involved in outbreaks caused by pathogenic bacteria, which increases the demand for new and efficient strategies to control transmission of shellfish infection. Bacteriophage (or phage) therapy represents a promising, tailor-made approach to control human pathogens in bivalves, but its success depends on a deep understanding of several factors that include the bacterial communities present in the harvesting waters, the appropriate selection of phage particles, the multiplicity of infection that produces the best bacterial inactivation, chemical and physical factors, the emergence of phage-resistant bacterial mutants and the life cycle of bivalves. This review discusses the need to advance phage therapy research for bivalve decontamination, highlighting their efficiency as an antimicrobial strategy and identifying critical aspects to successfully apply this therapy to control human pathogens associated with bivalve consumption.

Application of Bacteriophages in Nanotechnology

Bacteriophages (phages for short) are viruses, which have bacteria as hosts. The single phage body virion, is a colloidal particle, often possessing a dipole moment. As such, phages were used as perfectly monodisperse systems to study various physicochemical phenomena (e.g., transport or sedimentation in complex fluids), or in the material science (e.g., as scaffolds). Nevertheless, phages also execute the life cycle to multiply and produce progeny virions. Upon completion of the life cycle of phages, the host cells are usually destroyed. Natural abilities to bind to and kill bacteria were a starting point for utilizing phages in phage therapies (i.e., medical treatments that use phages to fight bacterial infections) and for bacteria detection. Numerous applications of phages became possible thanks to phage display-a method connecting the phenotype and genotype, which allows for selecting specific peptides or proteins with affinity to a given target. Here, we review the application of bacteriophages in nanoscience, emphasizing bio-related applications, material science, soft matter research, and physical chemistry.

Electrospun nanofiber-based drug delivery platform: advances in diabetic foot ulcer management

INTRODUCTION

Electrospinning is a facile and viable method for the fabrication of nanofibers. Electrospun nanofiber has a great potential in providing local drug or therapeutic molecule delivery to the wound site. The versatile nature of this technique ensures a broad scope of material used in the fabrication of nanofibers.

AREA COVERED

A brief introduction to diabetic foot ulcer (DFU) is covered with its pathogenesis, followed by the role of electrospun nanofibers in DFU. This review covers the evolution of the electrospinning technique over the past few years, various types of electrospun nanofibers reported for DFU or chronic diabetic wounds, the challenges associated with the preparation of nanofibers, and various methods to evaluate their efficacy and performance in diabetic wound healing.

EXPERT OPINION

Electrospinning-based nanofibers provide a safe, effective, and multifunctional system for effective management of DFU.

Electrospun Nanofibers as Carriers of Microorganisms, Stem Cells, Proteins, and Nucleic Acids in Therapeutic and Other Applications

Electrospinning is a technique that uses polymer solutions and strong electric fields to produce nano-sized fibers that have wide-ranging applications. We present here an overview of the use of electrospinning to incorporate biological products into nanofibers, including microorganisms, cells, proteins, and nucleic acids. Although the conditions used during electrospinning limit the already problematic viability/stability of such biological products, their effective incorporation into nanofibers has been shown to be feasible. Synthetic polymers have been more frequently applied to make nanofibers than natural polymers. Polymer blends are commonly used to achieve favorable physical properties of nanofibers. The majority of nanofibers that contain biological product have been designed for therapeutic applications. The incorporation of these biological products into nanofibers can promote their stability or viability, and also allow their delivery to a desired tissue or organ. Other applications include plant protection in agriculture, fermentation in the food industry, biocatalytic environmental remediation, and biosensing. Live cells that have been incorporated into nanofibers include bacteria and fungi. Nanofibers have served as scaffolds for stem cells seeded on a surface, to enable their delivery and application in tissue regeneration and wound healing. Viruses incorporated into nanofibers have been used in gene delivery, as well as in therapies against bacterial infections and cancers. Proteins (hormones, growth factors, and enzymes) and nucleic acids (DNA and RNA) have been incorporated into nanofibers, mainly to treat diseases and enhance their stability. To summarize, incorporation of biological products into nanofibers has numerous advantages, such as providing protection and facilitating controlled delivery from a solid form with a large surface area. Future studies should address the challenge of transferring nanofibers with biological products into practical and industrial use.

Bacteriophages for Chronic Wound Treatment: from Traditional to Novel Delivery Systems

The treatment and management of chronic wounds presents a massive financial burden for global health care systems, with significant and disturbing consequences for the patients affected. These wounds remain challenging to treat, reduce the patients' life quality, and are responsible for a high percentage of limb amputations and many premature deaths. The presence of bacterial biofilms hampers chronic wound therapy due to the high tolerance of biofilm cells to many first- and second-line antibiotics. Due to the appearance of antibiotic-resistant and multidrug-resistant pathogens in these types of wounds, the research for alternative and complementary therapeutic approaches has increased. Bacteriophage (phage) therapy, discovered in the early 1900s, has been revived in the last few decades due to its antibacterial efficacy against antibiotic-resistant clinical isolates. Its use in the treatment of non-healing wounds has shown promising outcomes. In this review, we focus on the societal problems of chronic wounds, describe both the history and ongoing clinical trials of chronic wound-related treatments, and also outline experiments carried out for efficacy evaluation with different phage-host systems using in vitro, ex vivo, and in vivo animal models. We also describe the modern and most recent delivery systems developed for the incorporation of phages for species-targeted antibacterial control while protecting them upon exposure to harsh conditions, increasing the shelf life and facilitating storage of phage-based products. In this review, we also highlight the advances in phage therapy regulation.

Gold, Silver and Iron Oxide Nanoparticles: Synthesis and Bionanoconjugation Strategies Aimed at Electrochemical Applications

Nanomaterials have revolutionized the sensing and biosensing fields, with the development of more sensitive and selective devices for multiple applications. Gold, silver and iron oxide nanoparticles have played a particularly major role in this development. In this review, we provide a general overview of the synthesis and characteristics of gold, silver and iron oxide nanoparticles, along with the main strategies for their surface functionalization with ligands and biomolecules. Finally, different architectures suitable for electrochemical applications are reviewed, as well as their main fabrication procedures. We conclude with some considerations from the authors' perspective regarding the promising use of these materials and the challenges to be faced in the near future.

Antibacterial Efficiency of Surface-Immobilized Flavobacterium-Infecting Bacteriophage

Control of bacterial diseases by bacteriophages (phages) is gaining more interest due to increasing antibiotic resistance. This has led to technologies to attach phages on surfaces to form a biomaterial that can functionally display phages that interact with bacteria, to carry out successful infection cycles. Such a material could be applied in many environments where the target pathogens are expected. Although this approach has been applied successfully in a few studies already, the basis of the antibacterial effect by the immobilized phages is unclear, and the interpretation of the results depends on the study. Here, we studied the phage attachment density, their detachment rate, and infectivity on five different surfaces: silicon, amine-treated silicon, gold, carboxylate-treated gold, and cross-linker-activated carboxylate-treated gold. The density of attached phages varied between the different surfaces and was the highest on the cross-linker-activated carboxylate-treated gold. To understand whether the antibacterial effect is caused by the attached or the detached phages, the strength of the immobilization was analyzed by performing 3-12 washing steps. The detachment rates differed between the materials, with the amine-treated silicon surface generating the highest release of phages and maintaining the highest infectivity, even after extensive washing. However, covalent cross-linking seemed to interfere with the infectivity. Our results suggest that the detachment of the phages from the surface is a possible mechanism for the antibacterial effect. Furthermore, we introduce a measure of the infectivity by comparing the bacterial growth reductions produced by the phage-treated materials to the effect caused by a known number of free phages, resulting in a unit "effective PFU/surface area", a comparable standard between different studies.

The dawn of phage therapy

Bacteriophages or phages, being the most abundant entities on earth, represent a potential solution to a diverse range of problems. Phages are successful antibacterial agents whose use in therapeutics was hindered by the discovery of antibiotics. Eventually, because of the development and spread of antibiotic resistance among most bacterial species, interest in phage as therapeutic entities has returned, because their noninfectious nature to humans should make them safe for human nanomedicine. This review highlights the most recent advances and progress in phage therapy and bacterial hosts against which phage research is currently being conducted with respect to food, human, and marine pathogens. Bacterial immunity against phages and tactics of phage revenge to defeat bacterial defense systems are also summarized. We have also discussed approved phage-based products (whole phage-based products and phage proteins) and shed light on their influence on the eukaryotic host with respect to host safety and induction of immune response against phage preparations. Moreover, creation of phages with desirable qualities and their uses in cancer treatment, vaccine production, and other therapies are also reviewed to bring together evidence from the scientific literature about the potentials and possible utility of phage and phage encoded proteins in the field of therapeutics and industrial biotechnology.

In situ gelation of rhEGF-containing liquid crystalline precursor with good cargo stability and system mechanical properties: a novel delivery system for chronic wounds treatment

The objective of this study was to develop a novel delivery system for recombinant human epidermal growth factor (rhEGF) for chronic wound treatment.

Physisorption and chemisorption of T4 bacteriophages on amino functionalized silica particles

Bacteriophages, or phages, are receiving increasing interest as recognition tools for the design of bioactive surfaces. However, to maintain the activity of surface-bound phages, the immobilization strategy must provide the right orientation and not compromise the phages' integrity. The objectives of this study were to characterize the phage sorption capacity and the immobilized phage activity for aminated silica particles functionalized with T4 phages. Two functionalization strategies were compared; physisorption, based on electrostatic adhesion, and chemisorption, where the phage and the particle are coupled using a carbodiimide cross-linker. We report that chemisorption, at maximum adsorption conditions on 1 µm particles, yielded 16 functional phages per particle, which is 2.5 times more than by the physisorption method. Particle diameter is shown to have an important impact on phage attachment and 1.8 µm particles were found to have ∼4 times more phages per surface area than 0.5 µm particles. Higher surface coverage is attributed to the lower steric hindrance on bigger particles. These findings provide important guidelines for the design of phage-functionalized particles for environmental, biomedical, or sensing applications.

Antimicrobial and Osseointegration Properties of Nanostructured Titanium Orthopaedic Implants

The surface design of titanium implants influences not only the local biological reactions but also affects at least the clinical result in orthopaedic application. During the last decades, strong efforts have been made to improve osteointegration and prevent bacterial adhesion to these surfaces. Following the rule of “smaller, faster, cheaper”, nanotechnology has encountered clinical application. It is evident that the hierarchical implant surface micro- and nanotopography orchestrate the biological cascades of early peri-implant endosseous healing or implant loosening. This review of the literature gives a brief overview of nanostructured titanium-base biomaterials designed to improve osteointegration and prevent from bacterial infection.